Weatherability and adherence of polypropylene

ABSTRACT

A process is provided for improving the resistance to deterioration when exposed to weather and the adherence to other materials of polypropylene, particularly in the form of moldings, which comprises subjecting a surface of polypropylene to the action of activated oxygen gas at a temperature below about 100° C. in the presence of an N-alkyl or N-acyl 2,2,6,6-tetramethyl piperidyl compound for a time sufficient to improve such weather resistance and adherence.

This is a continuation of application Ser. No. 78,364, filed July 27, 1987, now abandoned.

Polypropylene resins have excellent mechanical properties, thermal properties and processability, in addition to being light in weight and relatively inexpensive, so that they find applications in a variety of molding shapes and sizes.

However, since polypropylene resins have inferior adherence to other materials, such as are used in coating compositions, their use in applications requiring that they be coated, printed or adhered to another material has inevitably been limited.

To improve the adherence of other materials to polypropylene resins, a specific primer coating has been applied to the polypropylene. However, primer coatings are expensive, and not always successful. Accordingly, a plasma surface treatment of the polypropylene using oxidizing gases has recently been suggested, to improve the adherability of the surface. By this method, the adherability of the surface of polypropylene resins has been improved to a practically sufficient level.

Polypropylene resins also have the disadvantage of poor weather resistance. Moldings which are used outdoors, such as automobile bumpers, must have good weatherability, and to do so, various kinds of stabilizers have been used.

Of these stabilizers, compounds containing 2,2,6,6-tetramethyl piperidyl groups in the molecule give the best stabilizing effects, and thus are usually added to moldings which are to be coated so as to prevent such degradation.

However, when a low temperature plasma treatment is applied to the surface of a polypropylene resin molding which contains a 2,2,6,6-tetramethyl piperidyl compound, to improve the adherability, the adherability is often degraded significantly, and after coating, the coating film can be peeled off or swelled out, raising serious problems.

In accordance with the present invention, these problems are overcome by subjecting a surface of polypropylene to the action of activated oxygen gas at a temperature below about 100° C. in the presence of a 2,2,6,6-tetramethyl piperidyl compound for a time sufficient to improve such weather resistance and adherence.

The 2,2,6,6-tetramethyl piperidyl compound contains at least one group having the formula: ##STR1## wherein R is selected from the group consisting of alkyl, hydroxyalkyl and alkoxy, having from about one to eighteen carbon atoms, alkylaryl having from seven to about eighteen carbon atoms, and acyl having from one to about eighteen carbon atoms.

The invention accordingly also provides polypropylene resin moldings having excellent weather resistance and adherence to other materials, comprising polypropylene and a compound having an N-alkyl or N-acyl 2,2,6,6-tetramethyl piperidyl group represented by the formula: ##STR2## wherein R is selected from the group consisting of alkyl having from one to about eighteen carbon atoms and acyl having from one to about eighteen carbon atoms, after having been subjected to such a low temperature plasma treatment.

The low temperature plasma treatment is effected at a temperature below about 100° C., and preferably at below about 50° C., by causing a low pressure oxidizing gas, oxygen or a mixture of oxygen with ozone, nitrogen, air, argon, carbon dioxide, chlorine, fluorine or bromine, to excite by high frequency electric discharge or microwave discharge, so as to generate an activated gas, and contacting the surface of the polypropylene moldings with the activated gas. Treatment time and gas pressure are not critical. An effective treatment is obtained at a gas pressure within the range from about 0.1 to about 10 torr for from about 5 seconds to about 15 minutes.

In the foregoing Formula (I), the R alkyl includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, octyl, 2-ethylhexyl, decyl, dodecyl, tetradecyl and octadecyl; alkylaryl include benzyl, phenylethyl, phenpropyl, phenbutyl, phenhexyl, phenoctyl, phendodecyl, hydroxyalkyl include hydroxyethyl, hydroxypropyl, hydroxybutyl, hydroxyhexyl, hydroxyoctadecyl; and alkoxy including ethoxyethyl and 2,3-epoxypropyl.

Exemplary R acyl include acetyl, propionyl, acryloyl, methacryloyl, butyroyl, octanoyl, decanoyl, dodecanoyl, octadecanoyl, benzoyl, 4-tertbutylbenzoyl, salicyloyl and phthaloyl.

The N-alkyl and N-acyl (or 1-alkyl and 1-acyl) 2,2,6,6-tetramethyl piperidine compounds of this invention are known compounds that as indicated have in the molecule the group: ##STR3##

Such 2,2,6,6-tetramethyl piperidine compounds, inter alia, are disclosed in the following illustrative patents:

Japanese patents Nos. 46-31733, 46-31734, 46-31735, 47-1628, 47-7380, 47-8539 and 48-12410; Japan kokai Nos. 46-5082, 47-590, 48-95986, 49-53570, 49-58085, 49-60337, 49-61236, 49-61238, 49-63738, 49-64634, 49-72332, 49-120492, 50-5435, 50-26779, 52-78876, 52-89677, 52-91875, 52-125175, 52-139071, 53-67749, 53-71082, 54-71185, 54-103877, 56-30985, 56-75488, 56-138189, 56-161387, 57-24393, 57-58681, 57-63359, 57-80453, 57-121034, 57-137358, 57-146755, 57-167316, 57-177022, 58-5319, 58-10568, 58-32642, 58-32864, 58-37025, 58-38720, 58-4703058-53931, 58-57444, 58-57445, 58-69879, 58-77862, 58-92660, 58-108238, 58-120646, 58-152053, 58-152881, 58-154739, 58-159460, 58 -168634, 58-194862, 58-194931, 58-201777, 58-206594, 58-210094, 58-217554;

U.S. Pat. Nos. 3,542,729, 3,640,928, 3,684,765, 3,705,126, 3,893,972, 3,925,376, 3,929,804, 3,940,401, 3,992,390, 3,899,464, 3,984,371, 3,971,795, 3,959,291, 3,993,655, 4,007,158, 4,038,280, 4,061,616, 4,086,204, 4,089,841, 4,096,114, 4,101,508, 4,102,858, 4,104,248, 4,104,251, 4,105,625, 4,107,139, 4,108,829, 4,110,334, 4,115,476, 4,116,927, 4,118,369, 4,128,608, 4,136,081, 4,140,673, 4,144,224, 4,148,784, 4,151,356, 4,154,722, 4,161,592, 4,162,246, 4,166,813, 4,173,599, 4,177,186, 4,185,007, 4,197,236, 4,198,334, 4,210,612, 4,219,465, 4,223,147, 4,234,728, 4,237,297, 4,238,388, 4,238,613, 4,276,401, 4,279,804, 4,288,593, 4,289,686, 4,293,466, 4,293,467, 4,293,468, 4,308,362, 4,309,546, 4,311,820, 4,312,804, 4,315,859, 4,316,025, 4,316,837, 4,317,911, 4,321,374, 4,322,531, 4,326,063, 4,331,586, 4,335,242, 4,336,183, 4,340,534, 4,348,524, 4,351,915, 4,356,279, 4,356,287, 4,356,307, 4,369,274, 4,369,321, 4,376,836, 4,378,443, 4,395,508, 4,400,513, 4,404,301, 4,405,735, 4,408,051, 4,412,021, 4,413,075, 4,413,076, 4,413,093 and 4,413,096.

Particularly preferred classes of 2,2,6,6-tetramethyl piperidyl compounds have the formulae II and III: ##STR4## wherein; R is selected from the group consisting of alkyl having from one to about eighteen carbon atoms; and acyl having from one to about eighteen carbon atoms;

X is ##STR5## Y is --O-- or --N(R₈)--; R₇ is alkyl having from one to about five carbon atoms;

R₈ is hydrogen or alkyl having from one to about eighteen carbon atoms;

R₁ is a residue of mono- or poly-carboxylic acid;

n is a number from 1 to about 6;

m is a number from 0 to about 5; and

n+m is from 1 to about 6;

R₂ is --O--R₈ or --N(R₈)R₉ ;

R₉ is alkyl having from one to about eighteen carbon atoms; and

R₈ and R₉ may be taken together to form alkylene or oxadialkylene;

R₃ is alkylene or ##STR6## R₄ is alkylene; and p is a number from one to about twenty; p represents the number of units in the polymer molecule of III,

Exemplary N-alkyl and N-acyl 2,2,6,6-tetramethyl piperidyl compounds include 1,2,2,6,6-pentamethyl-4-piperidylbenzoate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis(1-benzyl-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(1-acetyl-2,2,6,6-tetramethyl-4-piperidyl) sebacate, tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl) butanetetracarboxylate, tetrakis(1-octyl-2,2,6,6-pentamethyl-4-piperidyl) butanetetracarboxylate, tetrakis(1-acetyl-2,2,6,6-pentamethyl-4-piperidyl) butanetetracarboxylate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)-2-butyl-2-(3,5-ditert-butyl-4-hydroxybenzyl) malonate, bis(1-acryloyl-2,2,6,6-tetramethyl-4-piperidyl)-2-butyl-2-(3,5-di-tert-butyl-4-hydroxybenzyl) malonate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)di(tridecyl)butanetetracarboxylate, bis[1-(2,3-epoxypropyl)-2,2,6,6-tetramethyl-4-piperidyl]-di(tridecyl) butanetetracarboxylate, N-(1,2,2,6,6-pentamethyl-4-piperidyl) dodecyl succinic acid imide, 3,9-bis[1,1-dimethyl-2-tris (1,2,2,6,6-pentamethyl-4-piperidyloxycarbonyl) butylcarbonyloxyethyl]-2,4,8,10-tetraoxaspiro [5.5]undecane, 1,3,8-triaza-7,7,9,9-tetramethyl-3-dodecyl-8-acetylspiro [4.5] decane-2,4-di-one, bis(3-ethyl-8,8,9,10,10-pentamethyl-1,5-dioxaspiro [5.5]-3-undecylmethylether.

Small amounts of these compounds is effective. An amount within the range from about 0.001 to about 5 parts by weight, preferably from about 0.01 to about 3 parts by weight, per 100 parts by weight of the resin, is satisfactory.

Any polypropylene resin can be improved by the process of the present invention, including propylene homopolymers and random or block copolymers of propylene and an α-olefin which contain ethylene or other α-olefin in an amount from 1 to 30 wt. %, as well as blends of polypropylene with other olefin polymers and copolymers, such as low and high density polyethylene, ethylene/vinyl acetate copolymer, ethylene/propylene copolymer rubbers and styrene/butadiene blockcopolymer rubbers.

In addition, phenolic antioxidants, thioether antioxidants, organic phosphorus-containing compounds such as organic phosphites, and other ultraviolet light absorbers can be added to the polypropylene resin, as needed to improve resistance to oxidation and light.

Phenolic antioxidants which can be employed together with the stabilizer of the invention include 2,6-di-t-butyl-p-cresol, 2,6-di-phenyl-4-octadecyloxyphenol, stearyl(3,5-di-t-butyl-4-hydroxyphenyl)-propionate, distearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate, thio-diethylenebis(3,5-di-t-butyl-4-hydroxyphenylpropionate, hexamethylene-bis(3,5-di-t-butyl-4-hydroxyphenylpropionate, 4,4'-thiobis(6-t-butyl-m-cresol), 2-octylthio-4,6-bis(3,5-di-t-butyl-4-hydroxyphenoxy)-s-triazine, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylene-bis(4-ethyl-6-t-butylphenol), bis(3,3-bis(4-hydroxy-3-t-butylphenyl) butylic acid) glycol ester, 4,4'-butylidenebis (6-t-butyl-m-cresol), 2,2'-ethylidenebis(4,6-di-t-butylphenol), 2,2'-ethylidenebis(4-sec-butyl-6-t-butylphenol), 3,6-dioxaoctylenebis(3-methyl-5-t-butyl-4-hydroxyphenylpropionate), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl) butane, bis(2-t-butyl-4-methyl-6-(2-hydroxy-3-t-butyl-5-methyl benzyl)phenyl) terephthalate, 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-t-butylbenzyl) isocyanurate, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene, 1,3,5-tris((3,5-di-t-butyl-4-hydroxyphenyl) propionyloxyethyl) isocyanurate, tetrakis(methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate) methane.

The amount of phenolic antioxidant to be added is within the range from about 0.001 to about 5 parts by weight, and preferably from about 0.01 to about 3 parts by weight, per 100 parts by weight of the resin.

Thioether antioxidants which can be employed together with the stabilizer of the invention, include dialkylthiodipropionates, such as dilauryl-, dimyristyl- and di-stearylthiodipropionate, and esters of β-alkylthiopropionic acid with polyhydric alcohols, such as pentaerythritol tetrakis(β-dodecylthiopropionate).

Phosphite antioxidants which can be employed together with the stabilizer of the invention include trioctylphosphite, trilaurylphosphite, tridecylphosphite, octyl diphenylphosphite, tris(2,4-di-t-butylphenyl) phosphite, tris(nonylphenyl) phosphite, hexa(tridecyl) 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl) butane triphosphite, tetra(C₁₂₋₁₅ alkyl) 4,4'-isopropylidenediphenol diphosphite, tetra(tridecyl)4,4'-butylidenebis(3-methyl-6-t-butylphenol) diphosphite, hydrogenated-4,4'-isopropylidenediphenol polyphosphite, distearyl pentaerythritol diphosphite, phenyl 4,4'-isopropylidenediphenol pentaerythritol diphosphite, bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, di(nonylphenyl) pentaerythritol diphosphite and 4,4'-isopropylidenebis (2-t-butylphenol) di(nonylphenyl) phosphite.

Ultraviolet light absorbers which can be employed together with the stabilizer of the invention include hydroxybenzophenones such as 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone and 2,4-dihydroxybenzophenone; benzotriazoles such as 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chloro-benzotriazole, 2-(2'-hydroxy-5'-methylphenyl) benzotriazole and 2-(2'-hydroxy-3',5'-di-t-amylphenyl) benzotriazole; benzoates such as phenyl salicylate, p-t-butylphenyl salicylate, 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate and hexadecyl-3,5-di-t-butyl-4-hydroxybenzoate; Ni compounds such as 2,2'-thiobis(4-t-octylphenol) Ni salt, (2,2'-thiobis(4-t-octylphenolate))-n-butylamine Ni and (3,5-di-t-butyl-4-hydroxybenzyl) phosphonic acid monoethyl ester Ni salt; substituted acrylonitriles such as α-cyano-β-methyl-β-(p-methoxyphenyl) acrylic acid methyl ester; and oxanilides such as N-2-ethylphenyl-N'-2-ethoxy-5-t-butylphenyloxanilide and N-2-ethylphenyl-N'-2-ethoxyphenyloxanilide.

In addition, inorganic fillers such as talc, calcium carbonate and glass fiber, metal soaps such as calcium stearate and calcium stearoyl-lactate, nucleating agents, etc. may be added to the polypropylene resin of the present invention, as occasion demands.

The invention is applicable to polypropylene resin moldings formed in any desired shape by any melting method conventionally known per se in the art, such as injection molding, extrusion molding, blow molding, etc. The molding method constitutes no part of the present invention.

The following Examples represent preferred embodiments of the process and molded products of the invention.

EXAMPLES 1 TO 9

Molding compositions containing stabilizers of the invention and of the prior art were prepared by blending the following components uniformly in a high speed mixer:

    ______________________________________                                         Ingredients          Parts by Weight                                           ______________________________________                                         Propylene homopolymer                                                                               100                                                       Calcium stearate     0.1                                                       Tetrakis[methylene-3-(3,5-di-tert-butyl-                                                            0.1                                                       4-hydroxyphenyl)propionate] methane                                            2-(2'-Hydroxy-3'-tert-butyl-5'-methyl-                                                              0.2                                                       phenyl)-5-chlorobenzotriazole                                                  Stabilizer as shown in Table I                                                                      0.2                                                       ______________________________________                                    

The mixtures were extruded at 230° C. in a 50φ-uniaxial extruder, thereby preparing pellets. Test pieces of 100×100×3 mm were prepared by injection molding of the pellets.

The test pieces were treated in a microwave plasma treatment apparatus (TMZ-9602Z, product of Toshiba Corporation) at room temperature (25° C.) for 10 seconds at a flow rate of 400 cc/minute and a pressure of 0.5 torr, with activated oxygen gas and a power output of 400 W.

The test pieces after having undergone the plasma treatment were sprayed with twin pack polyurethane coating (R-263, product of Nippon Beechemical Co., Ltd.) to attain a film thickness of about 100 to 120μ. Thereafter, the coated test pieces were baked at 90° C. for 40 minutes.

Then, a strip of the coating film was cut out at a width of 10 mm, and the belt-shaped coating film strip then was peeled off from one end of the cut and folded in the opposite direction, thereby conducting a 180 degree peeling test at a pulling rate of 20 mm/minute. Further, after immersing a coated test piece in hot water of 40° C. for 10 days, it was observed whether or not the coating film was swelled.

Further, using a test piece uncoated and untreated and a test piece uncoated but treated, light stability was measured in a sunshine Weatherometer at 83° C. The results are shown in Table I:

                                      TABLE I                                      __________________________________________________________________________                              Hours to Failure                                                                           Peel                                                               Uncoated/                                                                            Uncoated/                                                                            strength                                  Example No.                                                                           Stabilizer        Untreated                                                                            Treated                                                                              (g/cm)                                                                              Swelling                             __________________________________________________________________________     Control 1                                                                             None               400   300  760  none                                 Control 2                                                                             Bis(2,2,6,6-tetramethyl-4-                                                                       2300  1500  370  severe                                      piperidyl) sebacate                                                     Control 3                                                                             Tetrakis(2,2,6,6-tetramethyl-4-                                                                  2500  1800  480  slight                                      piperidyl)butanetetracarboxylate                                        Example 1                                                                             Bis(1,2,2,6,6-pentamethyl-4-                                                                     2300  2000  640  none                                        piperidyl) sebacate                                                     Example 2                                                                             Bis(1-acetyl-2,2,6,6-tetramethyl-                                                                2200  2000  690  none                                        4-piperidyl) sebacate                                                   Example 3                                                                             Tetrakis(1,2,2,6,6-pentamethyl-4-                                                                2600  2300  730  none                                        piperidyl) butanetetracarboxylate                                       Example 4                                                                             Bis(1,2,2,6,6-pentamethyl-4-piperidyl)-                                                          2500  2300  720  none                                        di(tridecyl)butanetetracarboxylate                                      Example 5                                                                             1,3,8-Triaza-7,7,9,9-tetramethyl-8-                                                              2200  1900  680  none                                        acetylspiro [4.5] decane-2,4-dione                                      Example 6                                                                             3,9-Bis(1,1-dimethyl-2-(tris-                                                                    2500  2300  700  none                                        (1,2,2,6,6-pentamethyl-4-                                                      piperidyloxycarbonyl)butylcarbonyl-                                            oxy)ethyl)-2,4,8,10-tetraoxaspiro-                                             [5.5] undecane                                                          Example 7                                                                             Bis(1,2,2,6,6-pentamethyl-4-                                                                     2200  2000  620  none                                        piperidyl)-2-butyl-2-(3,5-di-t-                                                butyl-4-hydroxybenzyl) malonate                                         Example 8                                                                             Bis(3-ethyl-8,8,9,10,10-pentamethyl-                                                             2400  2100  690  none                                        1,5-dixoaspiro [5.5]-3-undecylmethyl)                                          ether                                                                   Example 9                                                                             N-(1,2,2,6,6-Pentamethyl-4-                                                                      2300  1900  700  none                                        piperidyl) dodecylsuccinimide                                           __________________________________________________________________________

From the results shown in Table I for Examples 1 to 9, it is apparent that the polypropylene resin moldings which contain a compound having an N-alkyl or N-acyl 2,2,6,6-tetramethyl piperidyl group are superior in light stability after plasma treatment, and also their adherence to coating film is not reduced, as compared with polypropylene resin moldings which contain a compound having the corresponding N-unsubstituted-2,2,6,6-tetramethyl piperidyl group.

EXAMPLES 10 TO 13

Molding compositions containing stabilizers of the invention and of the prior art were prepared by blending the following components uniformly in a high speed mixer:

    ______________________________________                                         Ingredients          Parts by Weight                                           ______________________________________                                         Ethylene/propylene random copolymer                                                                 100                                                       (ethylene content: 12 wt. %)                                                   Calcium stearate     0.05                                                      Tetrakis[methylene-3-(3,5-d-di-                                                                     0.05                                                      tertbutyl-4-hydroxyphenyl) propionate]                                         methane                                                                        2,6-di-tert-butyl-p-cresol                                                                          0.05                                                      Tris(2,4-di-tert-butylphenyl) phosphite                                                             0.1                                                       2-(2'-Hydroxy-3'-tert-butyl-5'-                                                                     0.2                                                       methylphenyl)-5-chlorobenzotriazole                                            Stabilizer shown in Table II                                                                        0.2                                                       ______________________________________                                    

The mixtures were extruded at 230° C. in a 50φ-uniaxial extruder, thereby preparing pellets. Test pieces of 100×100×3 mm were prepared by injection molding of the pellets.

The test pieces were treated in a microwave plasma treatment apparatus (TMZ-9602Z, product of Toshiba Corporation) at room temperature (25° C.) for 10 seconds at a flow rate of 400 cc/minute and a pressure of 0.5 torr, with activated oxygen gas and a power output of 400 W.

The test pieces after having undergone the plasma treatment were sprayed with twin pack polyurethane coating (R-263, product of Nippon Beechemical Co., Ltd.) to attain a film thickness of about 100 to 120μ. Thereafter, the coated test pieces were baked at 90° C. for 40 minutes.

Then, a strip of the coating film was cut out at a width of 10 mm, and the belt-shaped coating film strip then was peeled off from one end of the cut and folded in the opposite direction, thereby conducting a 180 degree peeling test at a pulling rate of 20 mm/minute. Further, after immersing a coated test piece in hot water of 40° C. for 10 days, it was observed whether or not the coating film was swelled.

Further, using a test piece uncoated and untreated and a test piece uncoated but treated, light stability was measured in a sunshine Weatherometer at 83° C. The results are shown in Table II:

                                      TABLE II                                     __________________________________________________________________________                              Hours to Failure                                                                           Peel                                                               Uncoated/                                                                            Uncoated/                                                                            strength                                  Example No.                                                                           Stabilizer        Untreated                                                                            Treated                                                                              (g/cm)                                                                              Swelling                             __________________________________________________________________________     Control 1                                                                             None               400   300  620  none                                 Control 2                                                                             Bis(2,2,6,6-tetramethyl-4-                                                                       2500  1800  340  severe                                      piperidyl) sebacate                                                     Control 3                                                                             Tetrakis(2,2,6,6-tetramethyl-4-                                                                  2700  2000  410  slight                                      piperidyl) butanetetracarboxylate                                       Example 10                                                                            Bis(1,2,2,6,6-pentamethyl-4-                                                                     2500  2200  510  none                                        piperidyl) sebacate                                                     Example 11                                                                            1,3,8-Triaza-7,7,9,9-tetramethyl-                                                                2300  2000  540  none                                        8-acetylspiro [4.5] decane-2,4-dione                                    Example 12                                                                            Tetrakis(1,2,2,6,6-pentamethyl-4-                                                                2800  2500  570  none                                        piperidyl) butanetetracarboxylate                                       Example 13                                                                            Bis(1,2,2,6,6-pentamethyl-4-                                                                     2700  2300  560  none                                        piperidyl)-di(tridecyl) butane-                                                tetracarboxylate                                                        __________________________________________________________________________

The results for Examples 10 to 13 demonstrate that the polypropylene resin moldings which contain a compound having an N-alkyl or acyl 2,2,6,6-tetramethyl piperidyl group are superior in light stability after plasma treatment and also their adherence to coating film is not reduced, as compared with polypropylene resin moldings which contain a compound having the corresponding N-unsubstituted-2,2,6,6-tetramethyl piperidyl group.

EXAMPLES 14 TO 17

Molding compositions containing stabilizers of the invention and of the prior art were prepared by blending the following components uniformly in a high speed mixer:

    ______________________________________                                         Ingredients           Parts by Weight                                          ______________________________________                                         Propylene homopolymer 90                                                       Ethylene-propylene rubber (EP02P,                                                                    10                                                       product of Japanese EP Rubber Co.)                                             Calcium stearate      0.05                                                     Tetrakis(methylene-3-(3,5-3-di-tert-                                                                 0.2                                                      butyl-4-hydroxyphenyl) propionate)                                             methane                                                                        2-(2'-Hydroxy-3'-tert-butyl-5'-methyl-                                                               0.2                                                      phenyl)-5-chloribenzotriazole                                                  Stabilizer shown in Table III                                                                        0.2                                                      ______________________________________                                    

The mixtures were extruded at 230° C. in a 50φ-uniaxial extruder, thereby preparing pellets. Test pieces of 100×100×3 mm were prepared by injection molding of the pellets.

The test pieces were treated in a microwave plasma treatment apparatus (TMZ-9602Z, product of Toshiba Corporation) at room temperature (25° C.) for 10 seconds at a flow rate of 400 cc/minute and a pressure of 0.5 torr, with activated oxygen gas and a power output of 400 W.

The test pieces after having undergone the plasma treatment were sprayed with twin pack polyurethane coating (R-263, product of Nippon Beechemical Co., Ltd.) to attain a film thickness of about 100 to 120μ. Thereafter, the coated test pieces were baked at 90° C. for 40 minutes.

Then, a strip of the coating film was cut out at a width of 10 mm, and the belt-shaped coating film strip then was peeled off from one end of the cut and folded in the opposite direction, thereby conducting a 180 degree peeling test at a pulling rate of 20 mm/minute. Further, after immersing a coated test piece in hot water of 40° C. for 10 days, it was observed whether or not the coating film was swelled.

Further, using a test piece uncoated and untreated and a test piece uncoated but treated, light stability was measured in a sunshine Weatherometer at 83° C. The results are shown in Table III:

                                      TABLE III                                    __________________________________________________________________________                              Hours to Failure                                                                           Peel                                                               Uncoated/                                                                            Uncoated/                                                                            strength                                  Example No.                                                                           Stabilizer        Untreated                                                                            Treated                                                                              (g/cm)                                                                              Swelling                             __________________________________________________________________________     Control 1                                                                             None               400   300  630  none                                 Control 2                                                                             Tetrakis(2,2,6,6-tetramethyl-4-                                                                  2300  1600  430  slight                                      piperidyl) butanetetracarboxylate                                       Example 14                                                                            Bis(1,2,2,6,6-pentamethyl-4-                                                                     2100  1700  520  none                                        piperidyl) sebacate                                                     Example 15                                                                            Tetrakis(1,2,2,6,6-pentamethyl-4-                                                                2400  2200  580  none                                        piperidyl) butanetetracarboxylate                                       Example 16                                                                            Bis(1,2,2,6,6-pentamethyl-4-                                                                     2300  2100  560  none                                        piperidyl)-di(tridecyl) butane-                                                tetracarboxylate                                                        Example 17                                                                            3,9-Bis(1,1-dimethyl-2-(tris-                                                                    2300  2000  580  none                                        (1,2,2,6,6-pentamethyl-4-                                                      piperidyloxycarbonyl) butylcarbonyl-                                           oxy) ethyl)-2,4,8,10-tetraoxaspiro-                                            [5.5] undecane                                                          __________________________________________________________________________

The results shown in Table III for Examples 14 to 17 demonstrate that the polypropylene resin moldings which contain a compound having an N-alkyl or acyl 2,2,6,6-tetramethyl piperidyl group are superior in light stability after plasma treatment and also do not have their adherence to coating film reduced, as compared with polypropylene resin moldings which contain a compound having the corresponding N-unsubstituted-2,2,6,6-tetramethyl piperidyl group. 

Having regard to the foregoing disclosure the following is claimed as the inventive and patentable embodiments thereof:
 1. A process for improving the resistance to deterioration when exposed to weather and the adherence to other materials of polypropylene which comprises subjecting a surface of polypropylene to the action of activated oxygen gas at a temperature below about 100° C. in the presence of an N-alkyl or N-acyl 2,2,6,6-tetramethyl piperidyl compound and a phenolic antioxidant for a time sufficient to improve such weather resistance and adherence.
 2. A process according to claim 1 in which the gas is a mixture of activated oxygen and a gas selected from the group consisting of air, argon, nitrogen, carbon dioxide, chlorine, fluorine and bromine.
 3. A process according to claim 1 in which the temperature is from 25° to about 50° C.
 4. A process according to claim 1 in which the time is from five seconds to about 15 minutes.
 5. A process according to claim 1 in which the polypropylene is polypropylene homo-polymer.
 6. A process according to claim 1 in which the polypropylene is a copolymer of propylene and another α-olefin.
 7. A process according to claim 1 in which the N-alkyl or N-acyl 2,2,6,6-tetramethyl piperidyl compound has an N-acyl or N-alkyl 2,2,6,6-tetramethyl piperidyl group that has the formula: ##STR7## wherein R is selected from the group consisting of alkyl having from one to about eighteen carbon atoms and acyl having from one to about eighteen carbon atoms.
 8. A process according to claim 7 in which R is alkyl.
 9. A process according to claim 7 in which R is acyl.
 10. A process according to claim 7 in which the 2,2,6,6-tetramethyl piperidyl compound is bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate.
 11. A process according to claim 7 in which the 2,2,6,6-tetramethyl piperidyl compound is tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl) butanetetracarboxylate.
 12. A process according to claim 7 in which the 2,2,6,6-tetramethyl piperidyl compound is bis(1,2,2,6,6-pentamethyl-4-piperidyl)-di(tridecyl) butanetetracarboxylate.
 13. A process according to claim 7 in which the 2,2,6,6-tetramethyl piperidyl compound is 3,9-bis(1,1-dimethyl-2-(tris(1,2,2,6,6-pentamethyl-4-piperidyloxycarbonyl) butylcarbonyloxy)ethyl)-2,4,8,10-tetraoxaspiro-[5.5] undecane. 